The present invention relates to precision linear motion systems and more particularly it relates to a structural element for precision linear motion systems.
Precision linear motion is required in many types of products such as machine tools, photo plotters, laser welding or cutting machines and robots. To achieve precision linear motion, it is necessary to provide a base for the linear guide system that is structurally stiff enough to minimize deflection caused by the loads carried by the system and cutting forces, if present. In addition, the structure must be dimensionally stable for a period of many years.
The most common material used for precision linear motion systems in the past and in wide use today is cast iron. Many other materials are also used including steel weldments, granite, artificial granite and concrete. With the increasing speed of industrial processes including machining speeds in machine tools, there is demand for lighter structures. Reducing the mass of moving structures reduces the servo power required and increases the sensitivity and dynamic accuracy of the system. There are also secondary benefits to lighter structures including lower shipping costs, lower manufacturing costs and reduced power requirements.
Cast iron, granite and artificial granite structures are heavy by their very nature and cannot be made lightweight due to limitations of the material itself or the processes used to make them. Steel weldments can be made relatively light in weight but experience has shown that they lack long term stability due to the stresses induced by extensive seam welding and are expensive to fabricate and machine.
Traditional materials utilized for manufacturing the components of precision linear motion systems lend themselves to accurate machining in order to obtain a precisely aligned mounting of a way system to the structural elements of the precision linear motion systems. Problems of achieving the necessary precise alignment have resulted when other materials have been used.
An example of such a steel weldment is taught by U.S. Pat. No. 2,789,480, which discloses fabricated structure made of a formed steel plate outer wall with a series of formed steel strips which are bent in a V-shape such that the vertices of the V-shaped strips are welded to the outer wall. In such a structure all of the formed steel elements are seam welded. U.S. Pat. No. 4,177,550 also shows a machine tool having hollow structural steel members which are welded together to form unitary structures. The inventive structure here is also a typical steel weldment which requires expensive and extensive seam welding. Both of the structures taught by these patents require complex welding operations and expensive machining on large machine tools after fabrication.
It is therefore a principal object of the present invention to provide structural components for linear motion systems that weigh significantly less than cast iron, steel weldment or other alternatives yet still provide the necessary rigidity for many applications.
Another object of the present invention is to provide a structural component for linear motion systems which has a simple construction that relies primarily upon spot welding for assembly.
Still another object of the present invention is to provide a very economically constructed machine tool component which may be utilized in machinery requiring linear way systems and which avoids costly machining on large components in order to attach the linear way systems.